1. Field of the Invention
The present invention relates to a Co—Cr—Mo alloy fine wire used in prosthetic materials for artificial bone, porous artificial bone material, porous embedded parts for medical and surgical purposes, wire and cable for bonding and fixing bone, bone bonding and fixing band processed by weaving or knitting fine wires, wire mesh and guide wire for stents for blood vessels, blood vessel plugging wire, and other medical implant devices, and relates to manufacturing methods, and relates to planar bodies and the like formed by processing this fine wire, and more particularly to a manufacturing technology for Co—Cr—Mo alloy fine wire having excellent biocompatibility, corrosion resistance, wear resistance, processability, and flexibility.
2. Related Art
Hitherto, a Co—Cr—Mo alloy has been known as a biocompatible alloy, but does not have good plastic processability, and hence the use of ingot and forged material thereof has been limited to rigid products of relatively large size, and it has been difficult to manufacture a fine wire suitable for biomaterials. However, since this alloy is excellent in biocompatibility, its application fields are wide, and it has been particularly demanded in the medical field. There has been a keen demand for development of fine wire made of this alloy having strength, wear resistance, and torsional rigidity conforming to dynamic characteristic of biomaterials, and flexibility fitting to the shape of biomaterials.
To meet such demands, a technology realizing plastic working by adding Ni to this alloy has been proposed (see patent reference 1, Japanese Laid-open Patent No. H10-43314). Specifically, by manufacturing a long member of Co—Cr—Mo containing Ni by less than 5 weight %, a transplantable medical device can be presented. However, Ni is allergenic, and it is preferred not to contain Ni in fine wire used in the medical field. According to the technology disclosed in patent reference 1, fine wires not containing Ni are also included, but only those containing Ni are shown in the embodiments of the detailed description of the invention, and it is not known whether or not Ni-free fine wire can be processed.
In this alloy, by increasing the Mo concentration and homogenizing the structure, both corrosion resistance and wear resistance are improved outstandingly, but in an ordinary ingot, as the Mo concentration increases, a stiff and brittle phase of high Mo concentration separates. As a result, at the time of plastic working, the working stress increases suddenly in the segregation phase, and cracking may occur, depending on the case, in the segregation phase or at the interface of segregation phase and matrix phase, and plastic working is difficult.
To solve this problem, a new technology is disclosed (patent reference 2, Japanese Laid-open Patent No. 2002-363675), that is, a molten alloy of Co—(26 to 30) weight % Cr—(6 to 12) weight % Mo—(0 to 0.3) weight % C is quenched and cast in a water-cooled copper die, the obtained material is processed by a hot forging method, and precipitates of high Mo concentration and second phase such as intermetallic compound are finely dispersed in grains of mean grain size of 50 micrometers or less, and by adjusting the structure in this manner, the plastic working performance is improved. If, however, an attempt is made to obtain a fine wire of 200 micrometers or less in diameter from the alloy of patent reference 2 by plastic working, if the second phase of high concentration Mo disperses granularly and finely, it is likely to be deformed, and only the second phase moves in the matrix phase (first phase), and the matrix phase may be damaged or holes and cracks may be formed in the matrix phase. Accordingly, to finish the alloy into a fine wire without causing such problems, it has been required to repeat the plastic working gradually in the structure control condition mentioned in patent reference 2. As a result, the number of steps is increased substantially, and the manufacturing cost increases.
In the prior art, further, as is clear from the description of claim 13 in the patent reference 1 and the corresponding embodiment of patent reference 1, no example is shown about the manufacture of fine wire with Mo content of 8 weight % or more, and there has been a strong demand for development of Ni-free fine wire with Mo content of 8 weight % or more, which is superior in corrosion resistance, wear resistance, and flexibility.
On the other hand, in the repeating method of forging as in the manufacturing method disclosed in patent reference 2, it is not easy to manufacture a fine wire of circular cross section, but it is rather possible to manufacture a flat band. It is also possible to manufacture a flat band by a roll method of using rapid quenching means by ejecting the molten metal to the chilling roll side. However, this flat band is poor in flexibility when fitted to a complicated shape in a human body, and it has been desired to develop a band processed by weaving or knitting a fine wire having a high degree of roundness (minor diameter/major diameter) of lateral cross section in order to improve the flexibility.